ioo PRACTICAL ORGANIC CHEMISTRY The chloral hydrate is melted in a distilling flask (250 c.c.) and the fuming nitric acid added.* The mixture is heated carefully over a small flame until the reaction sets in. After a few minutes red fumes are evolved, consisting mainly of nitrogen tetroxide. The reaction proceeds without the application of heat, and is complete when, on warming the liquid, nitrous fumes cease to come off. The product is now distilled ; below 123° excess of nitric acid distils ; between 123° and 194° n. mixture of trichloracetic acid and a small quantity of nitric acicl pass over, and at 194—196° nearly pure trichloracetic acicl collects in the receiver and solidifies on cooling. It is advisable to distil the last fraction with a condenser-tube only. The fraction boiling at 123—190° is treated with a fresh quantity of fuming nitric acid (10 c.c.), and the product- purified as before. Yield, 10—15 grams. CC13.CO.H + O = CC13.CO.OH. Properties.— Colourless, rhombohedral crystals ; m. p. 52° ; b. p. 195°. See Appendix, p. 257. PREPARATION 25. CO.OH Oxalic Acid, | +2H0O CO.OH Scheele (1776), Naumann, Moeser, Lindenbaum, /. Cham. 1907, 75, 146. 140 c.c. cone, nitric acicl. 20 grins, cane sugar. o'l grm. vanadium pentoxide. The nitric acid is warmed gently on the water-bath in a flask(i litre) with the addition of the vanadium pentoxide. It Is then placed in the fume cupboard and the cane sugar at onc<* added. As soon as torrents of brown fumes begin to be evolved, the flask is placed in cold water. After the reaction has ceasecl tli o liquid is left for twenty-four hours when colourless crystals of the acid separate. A further small quantity may be obtained from the mother liquor on standing. The crystals are drained on a small porcelain funnel without filter paper, and recrystallisecl from a very small quantity of water. Yield, 15—20 grams.